1. Field of the Invention
The present invention relates to a sheet feeding apparatus, and an image forming apparatus and an image reading apparatus which are respectively equipped with the sheet feeding apparatus.
2. Related Background Art
Conventionally, an image forming apparatus such as a copying machine, a printer, a facsimile machine or the like, or an image reading apparatus such as a scanner or the like is equipped with a sheet feeding apparatus which feeds sheets to an image forming portion or an image reading portion. More specifically, in the sheet feeding apparatus like this, for example, the sheets stacked on a sheet stacking portion are fed to a sheet feeding means, the fed sheets are then separated one by one by a separating portion consisting of a separating roller and a separating pad, and the separated sheet is further conveyed to the image forming section or the image reading section.
Incidentally, as the conventional sheet feeding apparatus like this, there is an apparatus which is equipped with a stopper member rotating on, e.g., the upper point of a sheet conveying path so as to stop the sheets at a predetermined position when the sheets are stacked on the sheet staking portion. Thus, in this apparatus, the sheets are stacked when the stopper member is at the position to block up the sheet conveying path so that the stacked sheets abut against the stopper member, whereby the sheets are stopped at the predetermined position.
Here, in the case where the stopper member like this is provided, it is necessary to shift the stopper member to its initial position after ending the sheet conveying. In this context, as the construction for controlling the position of the stopper member, a construction for controlling the position of the stopper member without using a solenoid and an electromagnetic clutch being electrical actuators, and a mechanical spring clutch has been proposed (see Japanese Patent Application Laid-Open Nos. 2001-022137, H09-240862 and H09-058891).
In the above construction, for example, a driving source of a sheet conveying means is used as the driving source for controlling the position of the stopper member, and driving to the stopper member is transmitted through the sheet conveying means, whereby it is possible to prevent from transmitting excessive driving force. Thus, the above construction achieves the stopper member position controlling without using the electrical actuator and the spring clutch. Consequently, by not using the electrical actuator and the spring clutch as above, the above construction achieves space saving, cost reduction, and load reduction to a power supply substrate. Moreover, the above construction achieves achieve the high-reliability stopper member position controlling with extremely less number of parts.
However, in the conventional sheet feeding apparatus and the image forming and reading apparatuses respectively equipped with the conventional sheet feeding apparatus, after discharging all the sheets and before inserting a next sheet, it is necessary to execute an initialization operation to return the stopper member to its initial position preceding the stacking of the sheets so as to prepare a control function for the sheet leading edges. Here, to return the stopper member to its initial position, it is necessary to reverse a motor.
Incidentally, in Japanese Patent Application Laid-Open No. 2001-022137, when the stopper member is returned to its initial position and fixed, a large load is applied to the engaging arm portion of the stopper member, whereby it is necessary to sufficiently enlarge the stopper member (i.e., the engaging arm portion thereof) to maintain the intensity thereof. Moreover, there is a problem that the cost of the motor increases because large torque is necessary for the motor.
Further, in Japanese Patent Application Laid-Open No. H09-240862, it is necessary to surely reverse the motor as many as a predetermined rotation number to return the stopper member to its initial position. For this reason, there is a problem that the above controlling for the stopper member position is not applicable to the apparatus in which reverse rotation of the motor is executed for another use, that is, the use other than the return of the stopper member to its initial position.
Furthermore, in Japanese Patent Application Laid-Open No. H09-058891, the initial position of the stopper member is recognized by a sensor of primarily detecting whether an original (sheet) exists. However, in such a construction, turning on and off of the sensor are repeated intermittently even after a last original passed the stopper member, whereby interrupt processes of software frequently occur. Thus, the overall process might become heavy. Moreover, it is likely that the sensor is turned on because the position of the stopper member shifts due to opening and closing of an original guide. In this case, there is a problem that it is difficult on software to discriminate whether the original has been inserted or the stopper member is not on its initial position.